1. Field of the Invention
The present invention relates to an observation device and an observation method.
2. Description of the Related Art
Charged particle microscopes have an extremely higher resolution than optical microscopes, and have been widely used to clearly observe a microscopic structure of an object to be observed. In a charged particle microscope, an enlarged image of the object sample is obtained by radiating an object sample with a charged particle beam, and detecting particles discharged from the object sample, or particles transmitting the object sample (charged particles of the same type or a different type from the irradiated charged particles, an electromagnetic wave, or photons) by a detector.
Especially, in a process of manufacturing a semiconductor, a charged particle microscope such as a scanning electron microscope, a scanning ion microscope, or a scanning transmission electron microscope is used for inspection of semiconductor wafers, measurement of a pattern size, measurement of a pattern shape, and the like. In these uses, observation of a semiconductor pattern or a defect, detection of the defect, and analysis of a cause of the defect, measurement of the pattern size, and the like are performed using a captured image.
In the charged particle microscope, it is important to provide an image that enables easy observation and analysis. Thus, it is necessary to display the image that allows a portion to be observed, analyzed, and the like (hereinafter, a region of interest (ROI)) to be easily viewed. As examples of an ROI include a region in which a defect on a semiconductor appears, a region in which a pattern to be observed appears, and the like. An image captured by the charged particle microscope may include a plurality of ROIs. To easily view an ROI, a plurality of images is often obtained where capturing conditions, an object to be captured, a position of a captured image, and the like are changed. Further, the detector has a plurality of types, such as a secondary charged particle detector, a backscattering particle detector, a detector that detects only specific particles or light, a detector that detects particles having energy or a spin direction within specific ranges, and the like. Information obtained by the individual detectors differs. Further, obtained information differs according to positions where the detectors are arranged, and thus many microscopes include a plurality of detectors of the same type or different types. If there is a plurality of microscopes, a plurality of captured images can be obtained by single image capturing.
To obtain an image having high visibility, a method of integrating a plurality of captured images has been proposed. For example, JP-2006-190693-A discloses “a charged particle beam device that includes a means to change a focus of a charged particle beam discharged from a charged particle source, a means to detect charged particles obtained in an irradiated portion of the charged particle beam of the sample, and a means to compose a secondary image of the sample as viewed from a charged particle beam source direction based on a signal of a portion where the charged particle beam is focused among signals output from the charged particle detector” (Abstract).
Further, JP-2010-62106-A discloses a method of “capturing a sample under different capturing conditions and obtaining a plurality of images of the sample, generating deterioration functions of the plurality of obtained images, respectively, generating an image in which the resolution has been improved using the plurality of obtained images and the generated deterioration functions corresponding to the images, and processing the image, in which the resolution has been improved” (Abstract).
Further, a method of integrating captured images in order to improve the visibility of an ROI has been proposed. Re-publication of PCT International Publication No. WO-2010/106837 discloses a pattern inspection device “that can make the specific gravity of the collation result image 74 higher in the known defect mode and the normal part, and can make the specific gravity of the detected image 71 higher otherwise, so as to generate a more natural review image 82” (Paragraph 0043), and a pattern inspection device “that can realize a composed image that further reflects the information of the detected image 71” by a morphing technique that is “a technology to compose the images such that the corresponding relationship between characteristic points of the images to be composed is maintained” (Paragraph 0044).
JP-2012-226842-A discloses a method of capturing an image of a sample using a charged particle microscope device, which directs “to capture an image having high image quality with respect to a region where a sufficient signal amount cannot be obtained from the sample, such as a lower layer region in a multilayer, or a bottom of a hole of a hole pattern”, and the method of capturing an image includes: a first image acquisition step of setting a gain of a detector of the charged particle microscope device as a first gain value and scanning the sample with a charged particle beam, and acquiring a first image; a second image acquisition step of setting a gain of the detector to a second gain value different from the first gain value and scanning the sample with the charged particle beam, and acquiring a second image; and an image composing step of composing the first image and the second image.